There is evidence suggesting that smokers persist in the use of nicotine gum beyond the recommended period of use. Furthermore, although the use of gum has improved the rate of successful smoking cessation, between 50-70% relapse to smoking. One of the factors which may contribute to the persistent use of gum or relapse to smoking may be the occurrence of withdrawal symptoms upon cessation of nicotine gum. We have spent the past several years determining valid, reliable and sensitive indicators of the tobacco withdrawal syndrome and how it is related to treatment outcome. The proposed research will extend our previous studies and examine signs and symptoms of withdrawal from nicotine gum and their relationship to treatment outcome. There will be four studies conducted over the course of four years. The first study will be a prospective and systematic examination of physiological, subjective, and behavioral reactions to nicotine gum cessation, and will compare the intensity and time course of signs and symptoms of withdrawal from nicotine gum with that of tobacco. The second study will be a prospective epidemiological survey which will determine the prevalence of nicotine gum withdrawal symptoms, determinates of severe withdrawal symptoms from nicotine gum, and the relationship between severity of nicotine withdrawal symptoms and relapse to smoking. The third study will examine the relationship between duration of nicotine gum use with severity of nicotine gum withdrawal symptoms and treatment outcome. The fourth study will examine the effect of gradual vs abrupt cessation of nicotine gum on severity of withdrawal symptoms and treatment outcome.